1. Field of Invention
The present invention relates generally to methods and apparatus for use in semiconductor fabrication. More particularly, the present invention relates to methods and apparatus for using a multiple pole configuration in an electrostatic chuck arranged to support a semiconductor wafer during semiconductor fabrication.
2. Description of the Prior Art
In the manufacture of semiconductor devices, the reliability and the repeatability of fabrication processes is crucial. That is, consistency in semiconductor fabrication is important to ensure that the final semiconductor product is robust and functions as intended. The overall fabrication of semiconductor devices generally includes processes such as etching, polishing, and deposition. As will be appreciated by those skilled in the art, etching processes, polishing processes, and deposition processes typically require that a semiconductor wafer is securely held, e.g., clamped.
In general, mechanical devices may be used to clamp a wafer during processing. FIG. 1 is a diagrammatic cross-sectional representation of a conventional mechanical device used to clamp a semiconductor wafer during processing. A mechanical device 10 includes a base plate 14 and top plates 18. A semiconductor wafer 22 is held between base plate 14 and top plates 18. Specifically, wafer 22 is held such that a top surface 24 of wafer 22 contacts top plates 18, while a bottom surface 26 of wafer 22 rests against base plate 14.
The use of mechanical device 10 may cause inconsistencies in the overall processing of wafer 22. By way of example, during an etching process used to etch top surface 24, the portions of top surface 24 which contact top plates 18 may not be properly etched, as top plates 18 generally obscure at least a portion of top surface 24. In other words, the edges of top surface 24 which are in contact with top plates 18 may not be uniformly etched, thereby affecting the overall fabrication of semiconductors contained within wafer 22.
In order to eliminate contact between the top surface of a wafer and a clamping mechanism such as a top plate, electrostatic clamps, or chucks, are often used to secure a wafer that is being processed. An electrostatic chuck is generally arranged to use the force of attraction between a positive charge and a negative charge to produce a force that is sufficient to hold a wafer in place. In other words, an electrostatic chuck uses forces created between a positive charge and a negative charge to essentially clamp a wafer.
FIG. 2 is a diagrammatic representation of a bipolar electrostatic chuck device in accordance with prior art. A bipolar electrostatic chuck device 50 includes a base plate 54 and a positive electrode 58. As will be appreciated by those skilled in the art, base plate 54 typically holds a negative charge, while positive electrode 58 holds a positive charge. Base plate 54 and positive electrode 58 are generally separated by a first insulator 60. A second insulator 62 is arranged over base plate 54 and positive electrode 58 in order to insulate a semiconductor wafer 64 from electric charges associated with base plate 54 and positive electrode 58. Wafer 64 is held against second insulator 62 when an attraction between positive electrode 58 and base plate 54 causes an electrostatic attraction between wafer 64 and positive electrode 58.
A power source 66 is arranged to apply voltage to base plate 54 and to positive electrode 58. No voltage is applied directly to wafer 64. Instead, as previously mentioned, the attraction between positive electrode 58 and base plate 54 causes wafer 64 to be attracted to positive electrode 58. Hence, wafer 64 may be secured against second insulator 62.
First insulator 60 is typically composed of a material with a high dielectric constant, such as an insulating epoxy. Second insulator 62 is also typically composed from a material with a high dielectric constant, e.g., silicon dioxide or titanium dioxide. As will be appreciated by those skilled in the art, if either first insulator 60 or second insulator 62 and "breaks down," bipolar electrostatic chuck device 50 will fail, and wafer 64 will no longer be securely held. By way of example, when first insulator 60 breaks down, or degrades, positive electrode 58 will typically short against base plate 54, thereby causing a failure of bipolar electrostatic chuck device 50. Degradation of first insulator 60 may occur for any number of different reasons, including, but not limited to, extended exposure to chemicals such as chlorine and sulfur tetraflouride. Chlorine and sulfur tetraflouride are often present in plasmas used during semiconductor fabrication processes.
The failure of an electrostatic chuck device may cause significant problems. For example, when an electrostatic chuck device fails, the device must generally either be repaired or replaced, thereby causing downtime in the overall semiconductor fabrication process. Further, any semiconductor wafer which is mounted on an electrostatic chuck device at the time of failure may be damaged. Downtime in the overall semiconductor fabrication process is undesirable in that it affects the efficiency of the fabrication process, whereas damage to a semiconductor wafer may cause reliability issues in semiconductor devices formed from the wafer. Therefore, what is needed is an improved electrostatic chuck device that is less likely to fail catastrophically.